83 research outputs found
On melting of boron phosphide under pressure
Melting of cubic boron phosphide, BP has been studied at pressures to 9 GPa
using synchrotron X-ray diffraction and electrical resistivity measurements. It
has been found that above 2.6 GPa BP melts congruently, and the melting curve
exhibits negative slope -60(7) K/GPa, which is indicative of a higher density
of the melt as compared to the solid phase.Comment: 3 pages, 1 figur
Thermoelastic Equation of State of Boron Suboxide B6O up to 6 GPa and 2700 K: Simplified Anderson-Gr\"uneisen Model and Thermodynamic Consistency
p-V-T equation of state of superhard boron suboxide B6O has been measured up
to 6 GPa and 2700 K using multianvil technique and synchrotron X-ray
diffraction. To fit the experimental data, the theoretical p-V-T equation of
state has been derived in approximation of the constant value of the
Anderson-Gr\"uneisen parameter {\delta}T. The model includes bulk modulus B0
=181 GPa and its first pressure derivative B0' = 6 at 300 K; two parameters
describing thermal expansion at 0.1 MPa, i.e. a = 1.4x10-5 K-1 and b = 5x10-9
K-2, as well as {\delta}T = 6. The good agreement between fitted and
experimental isobars has been achieved to the absolute volume changes up to 5%
as compared to volume at standard conditions, V0. The fitted thermal expansion
at 0.1 MPa is well consistent with the experimental data, as well as with
ambient-pressure heat capacity cp, bulk modulus B0 and {\delta}T describing its
evolution with volume and temperature. The fitted value of Gr\"uneisen
parameter {\gamma} = 0.85 is in agreement with previous empiric estimations for
B6O and experimental values for other boron-rich solids
Crystal structure of dense pseudo-cubic boron allotrope, pc-B52, by powder X-ray diffraction
During past years, a number of reports have been published on synthesis of
tetragonal allotrope of boron, t-B52 phase. However, no unambiguous
characterization of the crystal structure has been performed to the present
time, while remarkable variation of the a/c lattice-parameter ratio raises
strong doubts about its uniqueness. Here the Rietveld refinement of the crystal
structure of the high pressure - high temperature boron phase synthesized by a
direct solid-state transformation of rhombohedral beta-B106 at 20 GPa and 2500
K has been reported for the first time. Although this boron allotrope belongs
to the t-B52 type, its structure can be considered as pseudo-cubic with the a/c
ratio of sqr(2)
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